Gut Microbiome in Inflammatory Bowel Disease and Other Chronic Immune-Mediated Inflammatory Diseases

<b><i>Background:</i></b> Since the description of the normal human gut microbiome in healthy individuals using broad-range polymerase chain reaction, there has been great advancement in the techniques used to conduct microbiome research and applications of this research across health, gastrointestinal diseases, and nongastrointestinal diseases. <b><i>Summary and Key Messages:</i></b> In inflammatory bowel disease (IBD), studies have reported gut dysbiosis meaning that the microbial composition, diversity, and richness are altered. Persons with IBD harbor on average 25% fewer microbial genes than healthy persons. Reduced diversity has been reported in both the fecal and mucosal microbiome of IBD. Crohn disease and ulcerative colitis are systemic diseases with immunological alterations in both intestinal and circulating compartments. As knowledge about the impact of the gut microbiome on the intestinal and systemic immune response has grown, researchers have begun exploring how the gut microbiome may impact on other systemic conditions. Considering the role of microbes especially on regulatory T cells, it was plausible that the gut microbiome may have a role in other chronic immune-mediated inflammatory diseases. In this review, studies of the gut microbiome in other chronic immune-mediated inflammatory diseases are discussed including how the information can inform our understanding of the gut microbiome in IBD.